1. Field of the Invention
The invention relates generally to the field of wellbore instruments and well logging methods. More specifically, the invention relates to systems and methods for operating electrically powered instruments in a well using a wired pipe string as a signal communication channel.
2. Background Art
Well logging instruments are devices configured to move through a wellbore drilled through subsurface rock formations. Well logging instruments include one or more sensors and other devices that measure various properties of the subsurface rock formations and/or perform certain mechanical acts on the formations, such as drilling or percussively obtaining samples of the rock formations and withdrawing samples of connate fluid from the rock formations. Measurements of the properties of the rock formations made by the sensors may be recorded with respect to the instrument axial position (depth) within the wellbore as the instrument is moved along the wellbore. Such recording is referred to as a “well log.”
Well logging instruments can be conveyed along the wellbore by extending and withdrawing an armored electrical cable (“wireline”), wherein the instruments are coupled to the end of the wireline. Extending and withdrawing the wireline may be performed using a winch or similar spooling device known in the art. However, such conveyance relies on gravity to move the instruments into the wellbore, which can only be used on substantially vertical wellbores. Those wellbores deviating from vertical require additional force to move through the wellbore.
There are several types of wireline instrument conveyance known in the art for the foregoing conditions. One conveyance technique includes coupling the wireline instruments to the end of a coiled tubing having a wireline disposed therein. The wireline instruments are extended into and withdrawn from the wellbore by extending and retracting the coiled tubing, respectively. A subset of such coiled tubing techniques includes preliminary conveyance of the wireline configurable well logging instruments to a selected depth in the wellbore. See, for example, U.S. Pat. No. 5,433,276 issued to Martain et al. However, the use of coiled tubing with wireline instruments is costly and is inherently limited by the amount of pushing force capable with the coiled tubing. As a result, the use of coiled tubing is typically problematic in extended reach wells.
Another well logging instrument conveyance technique includes coupling wireline instruments to the end of a drill pipe or similar threadedly coupled pipe string. A wireline is coupled to the instruments using a “side entry sub” which provides a sealable passage from the exterior of the pipe string to the interior thereof. As the pipe string is extended into the wellbore, the wireline is extended by operating a conventional winch. An example of the foregoing is described in U.S. Pat. No. 6,092,416 issued to Halford et al. and assigned to the assignee of the present invention. However, this conveyance technique is frequently unreliable as the wireline is positioned in the annulus and subject to crushing, splicing or other damage. For example, the wireline may become pinched between the drill pipe and the casing or wellbore. Another drawback to using drill pipe to convey the well logging instruments using procedures known in the art is that the cable disposed outside the pipe disturbs the operation of the sealing equipment and makes it difficult to seal the drill pipe to maintain fluid pressure.
Additionally, the well logging instruments may be positioned at the end of a drill pipe without use of a wireline cable. In such circumstances, each well logging instrument is provided with a battery and memory to store the acquired data. As a result, the well logging instruments cannot communicate with the surface while downhole. Therefore, the data acquired cannot be analyzed at the surface until the wireline instruments return to the surface. Without any communication with the surface, surface operators cannot be certain the instruments are operating correctly, cannot control the instruments while downhole, and the data cannot be analyzed until after the wireline instruments are removed from the wellbore.
Recently, a type of drill pipe has been developed that includes a signal communication channel. See, for example, U.S. Pat. No. 6,641,434 issued to Boyle et al. and assigned to the assignee of the present invention. Such drill pipe has in particular provided substantially increased signal telemetry speed for use with downhole tools, such as logging while drilling (“LWD”) instruments or measuring while drilling (“MWD”), over conventional signal telemetry, which typically is performed by mud pressure modulation or by very low frequency electromagnetic signal transmission.
It is also desirable to use wireline instruments in conjunction with the above mentioned wired drill pipe for a number of reasons. An important reason is to be able to convey the wireline instruments into wellbores having conditions making wireline conveyance impractical, while at the same time having sufficient telemetry bandwidth so that the signals generated by the wireline instruments may be monitored substantially in real time during operation thereof. It is also desirable to be able to control certain functions of the wireline instruments from the surface. Such functionality may not be practical using conventional drill pipe instrument conveyance of the type described in the Halford et al. '416 patent cited above unless the wireline is present in the well logging system. Deployment of the wireline in conjunction with using drill pipe can make the overall well logging procedure complex and difficult to perform. There exists a need, therefore, for wireline instruments to be operated using wired pipe strings for data and command communication.